Diffusion and strain relaxation in silicon/silicon-germanium/silicon structures studied with Rutherford backscattering spectrometry

The thermal stability of strained Si/Si1-xGex/Si structures grown by molecular beam epitaxy was investigated by resistive heating and in situ Rutherford backscattering spectrometry. Ge profiles obtained from a 50 nm Si1-xGex layer on a Si(100) substrate capped with 50 nm Si were evaluated for different Ge concentrations after sequential heating periods at a particular temperature between 850 and 1010° C. The diffusion coefficients, calculated from the increase in signal in the tail of the Ge profile, proved to be comparable to the value for Ge in bulk Si. A more pronounced decrease of the signal at the center of the Ge profile indicated a faster diffusion within the SiGe layer which was confirmed by analysis of the FWHM of the Ge profile. Ion channeling measurements were used to characterize tetragonal strain in the buried SiGe layers. Angular scans through the 111 direction were interpreted with Monte Carlo channeling calculations and used to study strain relaxation in dislocation-free and partially relaxed layers.